The interactions of silicalite-1 (S-1), titanium silicalite -1 (TS-1), Ti-Si gel and anatase with H2O2 were investigated by ESR technique. It was found that different Ti-O-2(-) species could be formed over TS-1 zeolite and Ti-Si gel, which are dependent on the local structures of Ti atoms. The decay of O-2(-) species on these samples depicted that O-2(-) species on framework Ti sites are much more unstable than O-2(-) species on dispersed extra framework Ti sites. The reaction of O-2(-) species with phenol confirmed that O-2(-) species on framework Ti sites are highly active. (C) 2000 Elsevier Science B.V. All rights reserved.